1. Field of Invention
The present invention concerns electrically conductive patterns, printed circuits for example. That electrically conductive patterns can be produced from metal foil applied to a base by etching away areas of the foil is already known. Due to the purity of its metal, a printed-circuit board produced in this way has the advantage of low resistance. Its high manufacturing cost, however, is a drawback.
2. Prior Art
Printed circuits can be produced essentially less expensively and more precisely by another method, which is also appropriate for multilayered electric circuits. The electrically conductive patterns are manufactured in this method by imprinting, especially screening, an insulating base in a conductive ink that has the consistency of a paste, a metallic-silver ink for example. The drawback of printed circuits of this type, however, is that, due to the binder in the paste and to the size of the particles, the ink is not satisfactorily conductive. It is accordingly common to print relatively thick impressions (8 to 12 mm thick). Furthermore, when silver ink is employed, the metal will migrate subject to moisture from one circuit path to an adjacent path and lead to leakage currents and even short circuits. It is accordingly necessary to protect the circuit paths with special films. Another drawback is that no components can be soldered to the strips (cf. DE 3 413 408).
Also known is a method of manufacturing printed circuits wherein a desired pattern is printed on an insulating base in an ink in the form of a paste that contains an activator and metal is deposited onto the printed sections out of a bath. The result is thin patterns of pure metal. In spite of this advantage, however, this procedure (DE 1 176 731), although it has been known for many years, has not been able to compete in practice with the two other approaches.
A method of printing electrically conductive patterns in an ink consisting of organometallic activators, organic solvents, fillers, and binders is known from German Patent 3 241 579.
In spite of the drawbacks of screened circuits of electrically conductive metal ink, especially silver, the approach has been proven practical in many applications where demands on the precision of a conductive structure are high. As the technology progresses, however, the need for precision increases. Extremely thin printed circuits that are also highly precise are required. One particular problem that occurs in satisfying these demands is how to attach narrow patterns securely and permanently enough to the base.
This requisite can, according to German Patent 3 733 002, be satisfied with an electrically conductive pattern that consists of a base with a particularly insulating surface and of a metal coating that is non-electrically deposited onto the surface out of a metallization bath along by means of an impressed substance that contains an activator, whereby the substance contains organometallic activators, fillers, organic solvents, and binders. Substances of this type will adhere tight to the surface of the substrate, and the circuit will not become unintendedly loose.
The drawback to such electrically conductive patterns is that the ends of the circuit paths cannot be loosened from the substrate to create free-standing metal connection sections. The connection and plug sections have accordingly been created up to now by a complicated method involving either attaching pins mechanically or stamping out clips.